Creation & EvolutionForum for the discussion of this important topic. This forum is open to non-believers. There is a Christians-only forum in the Christians-only section too.
StubbornMule asked this in another thread. Since he is a "newbie" he probably hasn't seen all the threads yet.
Biological evolution (the one we are talking about) encompasses changes in populations of organisms over generations.
As Arkikay pointed out, this happens mainly thru two mechanisms:
1. Natural selection
2. Genetic drift.
Of these natural selection is by far the most important. NS is responsible for all the designs in biological organisms. In fact, NS is an algorithm to get design. That means that NS is a series of steps that, if followed by an idiot without thinking, is guaranteed to give the result. In this case the result of the algorithm of NS is design.
Now, if you want to go into more detail as to how evoution happens, feel free to ask whatever specific questions you have.
__________________ "If sound science appears to contradict the Bible, we may be sure that it is our interpretation of the Bible that is at fault." Christian Observer, 1832, pg. 437
"Christians should look on evolution simply as the method by which God works." Rev. James McCosh, theologian and President of Princeton, 1890
Biological evolution (the one we are talking about) encompasses changes in populations of organisms over generations.
As Arkikay pointed out, this happens mainly thru two mechanisms:
1. Natural selection
2. Genetic drift.
Of these natural selection is by far the most important. NS is responsible for all the designs in biological organisms. In fact, NS is an algorithm to get design. That means that NS is a series of steps that, if followed by an idiot without thinking, is guaranteed to give the result. In this case the result of the algorithm of NS is design.
Now, if you want to go into more detail as to how evoution happens, feel free to ask whatever specific questions you have.
I wouldn't necessarily say "...natural selection is by far the most important. NS is responsible for all the designs in biological organisms." There is still a great deal of debate regarding the Neutral Theory, which in the words of its architect, Motoo Kimura, predicts that:
"...the great majority of evolutionary mutant substitutions at the molecular level are caused by random fixation, through sampling drift, of selectively neutral (i.e., selectively equivalent) mutants under continued mutation pressure."
(Lewin 99)
In fact, evidence gathered since the theory's proposition in the 1960s has indicated that it is in some degree accurate-- in particular, observed mutation rate data has strongly supported the Neutral Theory. (Lewin 101) While it is hard to say exactly to what degree the two theories combine, it is clear that the truth of the matter lies somewhere in the middle, far from either extreme, where neither selection nor fixation are "by far the most important."
While I hesitate to emphasize the importance that chance fixation plays in evolution with creationists lurking to misinterpret me, it seems accuracy is the most important factor. After all, no point in convincing a creationist that evolution really does function, only to have them find out about this stuff later and think we lied to 'em. :rolleyes: Just a minor quibble.
I wouldn't necessarily say "...natural selection is by far the most important. NS is responsible for all the designs in biological organisms." There is still a great deal of debate regarding the Neutral Theory, which in the words of its architect, Motoo Kimura, predicts that:
(Lewin 99)
In fact, evidence gathered since the theory's proposition in the 1960s has indicated that it is in some degree accurate-- in particular, observed mutation rate data has strongly supported the Neutral Theory. (Lewin 101) While it is hard to say exactly to what degree the two theories combine, it is clear that the truth of the matter lies somewhere in the middle, far from either extreme, where neither selection nor fixation are "by far the most important."
Lewin is talking about mutation rates. And yes, most mutations are "neutral" in that the changes either don't affect the protein at all (get same amino acid) or are apparently neutral to selection. However, that is a far cry from saying that characteristics result from chance fixation. There are two "Neutral Theories". This is one. However, by its very nature, the neutral theory discussed here can't produce designs. To be selectively neutral means that both alleles are equally good at the job. You can't get design that way.
Dawkins demolishes the Neutral Theory in The Blind Watchmaker.
Now, Kimura had another Neutral Theory. In this one speciation was caused by a mutation that produced reproductive isolation between populations and then selection worked on the two populations to diverge them in characteristics. This has absolutely been falsified by the data. Reproductive isolation is a result of changing characteristics that in turn are a result of natural selection.
While I hesitate to emphasize the importance that chance fixation plays in evolution with creationists lurking to misinterpret me, it seems accuracy is the most important factor.
The problem is that chance fixation doesn't work on a population size larger than about 10 breeding individuals. The chances of chance fixation become just too small and it takes way too long.
Mathematics. Futuyma page 393
Kimura and then Li and Gauer derived the probability of an allele being fixed in the population. The probability of fixation of an allele A2 where the fitness of the genotypes are: A1A1 = 1, A1A2 = 1 +s, and A2A2 = 1 +2s is:
P = 1 - e^2Nsq/1 - e^-4Nq where e = the base of natural logarithms = 2.718, N = effective population size, s = selection coefficient, and q = the initial frequency of the allele in the population. For a mutation, q = 1/2N
Where s = 0 (genetic drift) then the equation reduces to P = 1/2N. The influence on fixation is obvious. Double the population and you halve the probability. Any N > 50 really reduces P.
For instance, if N = 1,000 then P = 0.0005 by genetic drift.
However, if you have N = 1,000 and the selective advantage is small at s = 0.01 and A2 is a mutation so that its initial frequency is 1/2000, then P = 0.02. That is 40 times the probability of fixation by chance alone. And that is a small s. Most s are 0.1 or above.
Now you see why I said genetic drift is unimportant.
Now, you can also look at this as a neutral mutation has a 0.5 probability of eventually being fixed. That is, it will eventually either be totally removed from the population or be fixed. This is where Kimura bases his hopes. However, now we get to look at time frames. Shoot! That info is at home!
I'll get back to you but I've done this before. It turns out that the time required to get fixation in a decently sized population (>1,000) is so long that it exceeds by an order of magnitude the average lifespan of a species. IOW, there simply isn't enough time for the neutral mutation to become fixed by pure chance.
__________________ "If sound science appears to contradict the Bible, we may be sure that it is our interpretation of the Bible that is at fault." Christian Observer, 1832, pg. 437
"Christians should look on evolution simply as the method by which God works." Rev. James McCosh, theologian and President of Princeton, 1890
Last edited by lucaspa; 5th November 2003 at 10:15 AM.
edit- I just figured out your name "lucaspa" after reading your bio.
but then we have a new enigma... what does A stand for? I suspect something like Andrew, but I live in hope that his parents were fans of greek classics and A is for Agamemnon or something really cool like that
__________________ MSci MSc ARCS DIC PhD..... yes, I am bragging.
but then we have a new enigma... what does A stand for? I suspect something like Andrew, but I live in hope that his parents were fans of greek classics and A is for Agamemnon or something really cool like that
Hopes dashed!
__________________ "If sound science appears to contradict the Bible, we may be sure that it is our interpretation of the Bible that is at fault." Christian Observer, 1832, pg. 437
"Christians should look on evolution simply as the method by which God works." Rev. James McCosh, theologian and President of Princeton, 1890
Oh, hell, my entire post got erased somehow. To recap briefly:
Thanks for the information luscapa, very interesting. I haven't really read much on evolutionary biology besides Dawkin's The Selfish Gene and the Lewin text I cited-- in the latter, the Neutral Theory is given a much more favourable shine than your information suggests that it ought recieve. Sorry for attempting to correct you-- I was both unaware of your expertise in the area, and I was eager to actually use the new information I learned in one of my recent classes. (The Lewin book was one of the primary texts for my recent advanced seminar in philosophy of biology.) To clarify, is 'Mathematics' the title of the Futuyama text you're citing, or was that merely a header in your post? I would be interested in reading the actual analysis in full, because Lewin gives a much more favourable appraisal of the theory. Also, is the study you cited more recent than the 1996 publishing date of the Lewin book, or does my book just contain bad information?
~AA
__________________
As the last of the Three to make entrance to the upper planes, many feared his power, doubted his counsel, and spurned his aid. However, when the War of Angels came at last, all saw then what they had not before-- he who walks the middle way can shroud the light and blind the darkness both at once. And so, the heavens gave a final sigh as his sword was loosed, signaling judgment, rebirth, and the fall of all that was once cherished in the hearts of men and seraphim alike.
Oh, hell, my entire post got erased somehow. To recap briefly:
Thanks for the information luscapa, very interesting. I haven't really read much on evolutionary biology besides Dawkin's The Selfish Gene and the Lewin text I cited-- in the latter, the Neutral Theory is given a much more favourable shine than your information suggests that it ought recieve. Sorry for attempting to correct you-- I was both unaware of your expertise in the area, and I was eager to actually use the new information I learned in one of my recent classes. (The Lewin book was one of the primary texts for my recent advanced seminar in philosophy of biology.) To clarify, is 'Mathematics' the title of the Futuyama text you're citing, or was that merely a header in your post? I would be interested in reading the actual analysis in full, because Lewin gives a much more favourable appraisal of the theory. Also, is the study you cited more recent than the 1996 publishing date of the Lewin book, or does my book just contain bad information?
~AA
The "Mathematics" was just a heading. The discussion is from Douglas Futuyma's Evolutionary Biology, 1998. The dates aren't that different.
Archangel, I think we are talking about apples and oranges here. Lewin is noting that the huge amount of variation in populations does indeed support Kimura's contention that most mutations are neutral in regards to selection. However, it is a leap from that to say the Neutral Theory of evolution is supported.
Kimura's Neutral Theory is that at least half the mutations that eventually become fixed must do so by drift -- pure chance. That doesn't look likely given the equations that Kimura himself developed!
And neutral mutations, by definition, can't be adaptations (design). If they were adaptations, they would be under selection and their fixation not due to pure chance.
In small populations, under 10 breeding individuals, there is a better chance that neutral or even slightly deleterious mutations can be fixed by chance. This would be genetic drift.
The calculations are:
N = 1,000 individuals and A is deleterious and and s = -0.001, then P = 0.00004. This will increase if N is very small.
That's not a very high probability, but it would get larger if you decrease N in the larger equation I gave you.
__________________ "If sound science appears to contradict the Bible, we may be sure that it is our interpretation of the Bible that is at fault." Christian Observer, 1832, pg. 437
"Christians should look on evolution simply as the method by which God works." Rev. James McCosh, theologian and President of Princeton, 1890
Hopes dashed! 
Linear Mode
